The present invention relates generally to image processing systems, and more specifically to a system which models the lateral inhibition, energy normalization, and noise suppression processes in a generic vertebrate retina. This retinal model enhances edges, eliminates brightness variations in a scene (image) for a given object and background, and suppresses noise to the extent that objects (signals) are extracted from noise in an image processing system.
Mankind has tried for centuries to understand data acquisition and perception processes in animal visual systems. Just as the optical elements of the earliest cameras were modeled on their counterparts in the human eye (lens, iris, and retina etc), modern image processing systems can still be improved on the subtler aspects of the vertibrate retina. Accordingly, an effort has been to construct machines to perform some visual function with specific regard to its realization by living systems. For example, pattern recognition has been investigated for many decades. One reasonably successful method to do pattern recognition is based on correlation. A correlator compares patterns using a well defined mathematical process to decide whether the patterns are similar.
Studying the correlator as a model of the human visual system may be important because the human brain may be correlating visual data as part of the pattern recognition process. If correlators actually exist in the brain, other elements must be present to eliminate some of the shortcomings that correlators exhibit. The correlator problems considered here are uncontrolled illumination, object reflectivity and noise.
The task of enhancing pattern recognition systems with an image processing system based on a model of the human retina is alleviated, to some extent, by the systems described in the following U.S. Patents, the disclosures of which are incorporated herein by reference:
______________________________________ U.S. Pat. No. 3,964,021 issued to Tamches; U.S. Pat. No. 4,318,083 issued to Argyle; U.S. Pat. No. 4,716,312 issued to Mead et al. U.S. Pat. No. 3,016,518 issued to Taylor; U.S. Pat. No. 3,088,096 issued to Steinbuch; U.S. Pat. No. 3,187,304 issued to Taylor; and U.S. Pat. No. 3,701,095 issued to Yamaguchi et al. ______________________________________
Perhaps the most significant of the above-cited patents is the Tamches patent, which discloses an analog electronic system for preprocessing an optical pattern in a spatially modulated scene. The other patents disclose image and signal processing systems and optical pattern recognition systems.
The approach of making an electronic model of a vertibrate retina is more fully explored in the following four technical articles, the disclosures of which are specifically incorporated herein by reference:
an article by Frank S. Werblin entitled, "The Control of Sensitivity in the Retina," published in Scientific American, 228: p. 70-79 on January 1973; an article by K. Fukushima entitled "An Electronic Model of the Retina" published in Proc. of the I.E.E.E. on December 1987, p. 1950-1951; an article by Carver A. Mead et al. entitled "Real-Time Visual Computations Using Analog CMOS Processing Arrays" dated November 1987; and an article by K. Fukushima entitled "Visual Feature Extraction by a Multilayered Network of Analog threshold Elements" published in I.E.E.E. Trans. Syst. Sci. Cybernetics, Vol SSC-5 pp 322-333 on October 1969.
The present invention is greatly indebted to the above-cited Werblin reference which discloses retinal electrical characteristics including receptor cell response ranges and response amplitudes. While Werblin is excellent in its documentation of the electrical responses of retinal cells and retinal sensitivity, it does not apply this knowledge to image processing systems.
Both of the Fukushima articles discuss analog electronic models of a vertibrate retina and are exemplary in the art. While these analog systems are state of the art feature extraction and pattern recognition systems, a digital image processing system would have more adjustable flexibility than these systems, and would be an advance in the art.
Carver A. Mead et al describe a set of analog VLSI retina chips which are used in photoreception and processing. While it is encouraging to find such artificial vision systems being modeled on biological vision processes, the task remains to provide a digital image processing system which models the lateral inhibition, energy normalization, and noise suppression processes in a generic vertibrate retina. The present invention is intended to satisfy that need.